3HG 



MOLLUSCA. 



posterior marg-in to that of the opposite valve : these five pieces cover the whole of the cloak. From the place 

 where the ligament should be springs the fleshy peduncle. A strong adductor muscle unites the two valves near 

 their beaks. The mouth of the animal lies concealed behind them, and the posterior 

 end of the body, with all its little articulated feet, comes out a little further down, 

 between the first four valves. The widest spread species in our seas {Lepas anatifera, 

 Linn.) has got its name from havings given rise to a fable of its being the original oi 

 parent of the Barnacle-goose. They g'row attached to rocks, piers, to the bottom ot 

 ships, &c. We may distinguish the PolUcipes, Leach, which, besides the five prin- 

 cipal valves, has several small ones near the pedicle. In some species these valves 

 ahnost equal the primary in size. There is often an odd one opposite the normal 

 odd one. [Scalpellum, Leach, consists of thirteen valves, six on each side and one 

 dorsal ; and its peduncle is squamosa.] Chieras, Leach. — The cartilaginous cloak 

 incloses five valves, but of small size, so as not to occupy the whole surface. Otion, 

 Leach. — The cloak contains only two very small valves, with three little pieces which 

 scarcely merit that name ; and there are two tubular appendages in the shape of ears. 

 Tetralismis, Cuv., has only four paired valves encircling the aperture, two being 

 longer than the others. The animal is partly contained in the pedicle, which is wide 

 and hirsute. They are, in some degree, Balani without a tube. [Lithotrya, Sow., 

 is pedunculated like Anatifa, but has, at the base of the peduncle, a shelly appendage 

 analogous to the testaceous base of Balanus, and possesses besides a peculiarity not 

 to be found in any other genus of this class, that of penetrating stones for its habi- 

 tation.] Flpr. 19).— Ci.. eras Cr»i.chii. 



The Balanus, Briig., or Acorn-Shells. 

 The principal part of tlie shell consists of a testacous tube attached to various bodies, the aperture 

 of which is more or less closed by two or four valves. This tube is formed of various pieces or com- 

 partments, which appear to unloose or separate in proportion as the growth of the animal requires 

 additional room. The branchi£e, the mouth, the articulated tentacula, and the anal tube, differ little 

 from the same parts in the Anatifa. 



In Balanus, properly so called, the tubular portion of the shell is a truncated cone, formed of six outer valves, 

 separated by as many inner ones, three of which are narrower than the others. Their base is usually formed of a 

 calcareous lamina, fixed to various bodies. The four valves of the operculum close the aperture exactly. The 

 rocks, shells, and piers of all our coasts are, in a manner, covered with a species, the 

 Lepas balanus, Linn. 



There have been separated from these the Acasta, Leach, whose base is irregular, con- 

 vex outwardly, and not fixed : the greater number live within sponges. [Sowerby reunites 

 Acasta to Balanus.] Conia, Blainv., whose shell has only four exterior valves. [On the 

 contrary, in the Octomeris, Sow., the pieces or valves amount to eight.] Asema, Ranz., 

 whose shell has no well-marked exterior valves. Pyrgoma, Sav., whose shell forms a very 

 depressed cone, with only a very small aperture, almost as in a shell of the Fissurella. 

 OcAWoi/fl, Ranz., which have only three outer valves, and a bivalved operculum. Creiisia, 

 Leach, with four outer valves, and a bivalved operculum. M. de la Lamarck sepa- 

 rates, under the name of Coroniila, the depressed species in which the 

 valves are loosely cellular ; and under that of Tubic'mella, the species which 

 form an elongated cone, but narrowest at the base, and girded with rings that 

 mark the successive epochs of its growth. There are species of both genera 

 which plant themselves on the skin of Whales, and penetrate into their lard. 

 Diadema, Ranz.— The shell is almost spherical, and has only two small 

 valves, almost concealed in the membrane that closes their operculum. The 

 iipercula do not shut the aperture entirely without the aid of the mem- 



Fig. 197. — Conia radiata 



brane that unites them. They also live upon Whales ; and we often find Otions attached to their surface. 



